Geostatistical Assessment of Critical Raw Materials in Alto Lazio Geothermal Area

The move towards low-carbon energy has increased the need for critical raw materials and interest in alternative sources. Geothermal waters are one possible source because they can contain dissolved elements of economic interest. However, measurements from individual sites do not show how concentrations vary across the whole area. This study examines the spatial distribution of lithium (Li), boron (B), fluoride (F) and measured water temperature in Alto Lazio, central Italy, and their relationships with the geological setting. Data from previous hydrogeochemical studies were analysed using statistical and geostatistical methods. After examining spatial trends and fitting variogram models to log10-transformed values, ordinary kriging was used to produce maps of estimates and estimation variance. The strong correlation between Li and B also supported their joint estimation through cokriging. Li and B shared areas of higher estimated concentrations near the southwestern coast and west of Lake Bracciano. Fluoride showed a different pattern, with some overlap. Relationships with water temperature varied between water groups and sampling types, while those with regional heat flow were weak or absent. Higher concentrations were not limited to one surface rock type, indicating that surface geology alone could not explain the observed patterns. Cokriging preserved the main patterns shown by ordinary kriging. Over the common area compared, the mean estimation variance on the logarithmic scale was about 11% lower for Li in the cokriging output, while the mean variances for B were similar. This indicates lower average modelled uncertainty for Li, but does not demonstrate more accurate predictions. The results help identify areas for further sampling and geological investigation. They provide an initial basis for assessing the area, while further work is needed to establish whether the dissolved elements could be economically recovered.